44 MADREPORARIA. 



run l)ack a short way beyond the margin of the aperture into the ridges of the Goenenchyma, 

 Septa descend slantingly from the margin, and then bend round to bound a short cylindrical 

 fossa. Owing to the slope of the septa, the fossae are funnel-shaped, with a short cylindrical 

 basal portion. Columella prominent and oval, with a marked directive keel. Interseptal 

 loculi well marked, broad or narrow wedge-shaped according to the number of septa, in the 

 smaller calicles often petaloid, in the projecting calicles often sharply marked off peripherally 

 by the sudden ending of a ridge of the coenenchyma. 



Goenenchyma finely granular, ridge-and-furrow system visible with pocket-lens, most 

 marked on the projecting calicles. 



There are two specimens of this singular Turbinarian, both almost perfect discs, one 9 cm. 

 in diameter, with an irregular surface, and a young specimen 4' 5 cm. in diameter, perfectly 

 Hat. There is no visible stalk, the centre of the under surface of the disc being in contact 

 with a conglomerate mass forming the substratum. This mass is clasped at its edges by the 

 root-like processes which suggested the specific name. These root processes are but variations 

 of the flowings of the cosnenchyma which ordinarily thicken the stalk. The flat disc shape 

 of the corallum in this case has something to do with the production of these roots, which, in 

 the larger specimen, hang free of the substratum. There is not sufficient slope to cause the 

 fluids to run in towards the centre. Hence, on reaching the epithecal film * which spreads 

 outwards from beneath the centre of the disc, where it is in contact with the substratum, it 

 th-ops to form the rootlets above described, which may fork at their tips as if seeking 

 attachment. 



The younger specimen differs slightly in the character of the calicles fi'om the larger ; the 

 disc is, in the former case, very thin, so that the calicles, which do not project, are very shallow. 

 This makes the oval columella apjjcar much more prominent than is the case in the older and 

 thicker stock with deeper calicles. 



«, h. Great Barrier Eeef. Saville-Kent Coll. (Type.) 



Species 21. Turbinaria agaricia. (PI. IX. ; PI. XXXI. fig. 19.) 



Description. — Corallum .shield-shaped, round or oval, slightly concave ; stalk short, tliick, 

 eccentric ; margin thin, slightly and irregularly waved. Under side wrinkled. 



Calicles slightly and evenly protuberant, except in the base of the concavity where they 

 are immersed; slope slightly outwards, i. e. towards the growing edge. In some specimens 

 smaller and more crowded than in others. Margin of the protuberant aperture of irregular 

 thickness, often thicker on dorsal than on ventral side. Aperture round or elliptical, nearlj- 

 uniform in size on the same specimen, but diflering on different .specimens from 1-25 mm. to 

 2 mm. in diameter. Eighteen to twenty-four septa, which do not reach the half-radius 

 circle, bend round from the margin and slope downwards to form a cylindrical or slightly 

 funnel-shaped fossa. The septa may be tliiek and granular if the ridges of the cttiiencliyma 



* This secondary epitheca is not infrequent on the under surfaces of Turbinarians, and secni.s 

 to prepare the way for the attachments of innumerable organisms (see ante, p. 11). 



